Stable aromatic amine composition, a process for preparing color stable aromatic amines, and the production of light colored aromatic amine-based polyether polyols

ABSTRACT

This invention relates to stable aromatic amine compositions. These compositions comprise a) an organic compound containing at least one carboxylic acid group, and b) an aromatic amine. This invention also relates to a process for stabilizing the color of aromatic amines, and to the use of these aromatic amines as initiators for the preparation of polyether polyols.

BACKGROUND OF THE INVENTION

This invention relates to a stable aromatic amine composition comprisingan aromatic amine group containing compound and a small quantity of acarboxylic acid. The present invention also relates to a method forpreventing the discoloration of aromatic amine group containingcompounds, and to a process for the production of light colored aromaticamine based polyether polyols.

One of the problems or disadvantages associated with amine groupcontaining compounds is the tendency of these compounds to discolor.

Discoloration of some amine group containing compounds such as, forexample, ortho-toluenediamine (o-TDA), darken quickly upon exposure toair, while others such as, for example, aniline, are more stable anddarken slower over time. The aliphatic amine group containing compoundsalso discolor over time at room temperature, but generally speaking,these discolor at a much slower rate than the aromatic amine groupcontaining compounds.

U.S. Pat. No. 3,595,918 relates to the stabilization of tolylenediamine. This reference discloses that tolyenediamine can be stablizedagainst discoloration by the addition of an ascorbic acid in an amountof 0.05% to about 5% by weight. Ascorbic acid, isoascorbic acid andtheir mixtures are the only compounds disclosed as being suitable forstabilizing tolyene diamine. These two compounds are actually cycliclactones, not free carboxylic acids.

Amine group containing compounds are known to be suitable initiators forpreparing polyether polyols. Various amine initiated polyether polyolsand the process for their production are described in, for example, U.S.Pat. Nos. 3,264,268, 3,314,995, 3,446,848, 3,462,492, 3,499,009,4,209,609, 4,391,728, 4,421,871 and 4,562,290, and as described inBritish Patents 1,073,664, 1,311,095 and 1,398,185.

U.S. Pat. No. 4,877,879 describes the stabilization of polyether polyolsprepared from amine initiators in the presence of alkaline catalysts.This reference suggests that the addition of an excess amount of areducing agent, particularly formic acid, is effective in neutralizingthe alkaline catalyst, thereby stabilizing the reactivity of thepolyether polyol. This is described as being particularly effective foraliphatic amine initiators containing a tertiary nitrogen as theresultant polyether reacts with an alkylene oxide to yield a dark,color-forming quaternary amine complex.

The use of discolored amine group containing compounds as initiators inthe production of polyether polyols results in the polyether polyolsalso being discolored. The dark color of the resultant polyether polyolsis irreversible. Therefore, a means of preventing discoloration of aminegroup containing compounds and/or reducing the color of polyetherpolyols started from amine group containing compounds are commerciallydesirable.

One way of avoiding/preventing discoloration of these amine groupcontaining compounds and polyether polyols prepared from thesecompounds, is to immediately form polyether polyols from the amine groupcontaining compounds after distillation, before they come into contactwith air. This, however, requires that the amine group containingcompounds and the resultant polyether polyols be produced in the sameplant, with no time lapse between the point of distilling the aminecontaining compounds and when these are used as initiators to formpolyether polyols. Otherwise, stringent engineering measures arerequired to ensure that the amine compounds are oxygen-free at allpoints in the process between the time they are purified and used.Currently, it is necessary to keep the entire process totally undernitrogen to prevent and/or minimize this discoloration.

In accordance with the present invention, it was found that the additionof a relatively small quantity of certain groups of compounds toaromatic amine compounds surprisingly formed compositions which arestable against discoloration. This is true even after storing thetreated aromatic amine compositions in a 100° C. oven for 1 week.Polyether polyols can then be produced from these treated aromatic aminecompounds, without the derogatory color effects one would normallyexpect.

SUMMARY OF THE INVENTION

This invention relates to stable aromatic amine compositions comprising:

a) from 0.001 to 10% (preferably 0.1 to 1%, most preferably from 0.1 to0.5%) by weight, based on 100% by weight of component b), of at leastone organic compound containing at least one carboxylic acid group,wherein the organic compound contains from 1 to 20 carbon atoms,preferably from 1 to 10 carbon atoms, and most preferably from 1 to 6carbon atoms, and

b) at least one aromatic amine group containing compound.

The present invention also relates to a process for stabilizing thecolor of an aromatic amine group containing compound. This processcomprises 1) adding a) from 0.001 to 10% (preferably 0.1 to 1%, mostpreferably from 0.1 to 0.5%) by weight, based on 100% by weight ofcomponent b), of at least one organic compound containing at least onecarboxylic acid group, wherein the organic compound contains from 1 to20 carbon atoms, preferably from 1 to 10 carbon atoms, and mostpreferably from 1 to 6 carbon atoms, to b) at least one aromatic aminegroup containing compound. Ortho-toluenediamine is a preferred aromaticamine in which discoloration can be prevented or minimized by adding asmall quantity of one of these organic compounds.

The present invention also relates to a process for the production ofstable, light colored aromatic amine-based polyether polyols comprisingalkoxylating an aromatic amine group containing compound, wherein b)said aromatic amine group containing compound has been treated with a)from 0.001 to 10% (preferably from 0.1 to 1%, most preferably 0.1 to0.5%) by weight, based on 100% by weight of the aromatic amine groupcontaining compound, of at least one organic compound containing atleast one carboxylic acid group, wherein said compound contains from 1to 20 carbon atoms, preferably from 1 to 10 carbon atoms, and mostpreferably from 1 to 6 carbon atoms. The addition of a small quantity ofan organic compound containing at least one carboxylic acid group,wherein the compound contains from 1 to 20 carbon atoms is effective inpreventing or minimizing the discoloration of aromatic amine groupcontaining compounds, and thereby allows light colored polyether polyolsto be produced therefrom.

DETAILED DESCRIPTION OF THE INVENTION

As used in the present invention, the term stable with respect to thearomatic amine compositions of the present invention means that thecolor of these is lighter than the standard when stored for at least 1week at a temperature of ≧25° C. The standard is the correspondinguntreated aromatic amine. The treated amine compositions varied in colorfrom a pale pink to a ruby red, based on a visual assessment. Thesecolors were then defined by the reflectance values (L, a, b) using aHunterlab Color Questll unit.

In accordance with the present invention, suitable organic compoundscontaining at least one carboxylic acid group wherein the organiccompound contains from 1 to 20 carbon atoms (preferably from 1 to 10carbon atoms, most preferably from 1 to 6 carbon atoms) are suitable forpreventing discoloration of aromatic amine group containing compounds.The number of carbon atoms set forth above is intended to be inclusiveof the carbon atom in the carboxylic acid group(s). Suitable examples ofthese organic aliphatic compounds include, for example, mono- andpolycarboxylic acid groups, aliphatic compounds containing mono- andpolycarboxylic acid groups and at least one hydroxyl groups, aromaticcompounds containing mono- and polycarboxylic acid groups, aromaticcompounds containing mono- and polycarboxylic acid groups and at leastone hydroxyl group, and compounds containing mono- and polycarboxylicacid groups and one or more ether groups, amine groups or thio groups.

The suitable aliphatic compounds containing mono- and poly-carboxylicacid groups typically contain from 1 to 20 carbon atoms, inclusive ofthe carbon atoms present in the carboxylic acid group(s). It ispreferred that aliphatic compounds containing mono- and polycarboxylicacid groups contain from 1 to 20 carbon atoms and from 1 to 6 carboxylicacid groups. Suitable aliphatic groups may be branched or linear. Someexamples of these aliphatic compounds include formic acid, acetic acid,propionic acid, acrylic acid, butyric acid, valeric acid, oxalic acid,etc. Preferred compounds are formic acid and acetic acid.

Suitable aliphatic compounds containing mono- and poly-carboxylic acidgroups which additionally contain one or more hydroxyl groups typicallycontain from 2 to 20 carbon atoms, inclusive of the carbon atoms presentin the carboxylic acid group(s). It is preferred that aliphaticcompounds containing mono- and polycarboxylic acid groups and one ormore hydroxyl groups, contain from 2 to 20 carbon atoms, and from 1 to 6carboxylic acid groups, and from 1 to 8 hydroxyl groups. Suitablealiphatic compounds may be branched or linear. Some examples of thesecompounds include glycolic acid, citric acid, lactic acid, 12-hydroxystearic acid, gluconic acid, mucic acid, etc. A preferred compound isglycolic acid.

Suitable aromatic compounds containing mono- and poly-carboxylic acidgroups typically contain from 7 to 20 carbon atoms, inclusive of thecarbon atoms present in the carboxylic acid group(s). It is preferredthat aromatic compounds containing mono- and polycarboxylic acid groupscontain from 7 to 20 carbon atoms, and from 1 to 6 carboxylic acidgroups. It is not necessary for the carboxylic acid group(s) of thesecompounds to be attached directly to an aromatic ring. Some examples ofthese aromatic compounds include benzoic acid, phthalic acid,1,2,4,5-benzene-tetra-carboxylic acid, phenylacetic acid, phenylmalonicacid, etc. A preferred compound is benzoic acid.

The suitable aromatic compounds containing mono- and poly-carboxylicacid groups which additionally contain one or more hydroxyl groupstypically contain from 7 to 20 carbon atoms, inclusive of the carbonatoms present in the carboxylic acid group(s). It is preferred thataromatic compounds containing mono- and polycarboxylic acid groups andone or more hydroxyl groups, contain from 7 to 20 carbon atoms, and from1 to 6 carboxylic acid groups, and from 1 to 5 hydroxyl groups. Someexamples of these aromatic compounds include salicylic acid,4-hydroxyphenylacetic acid, mendelic acid, dihydroxyphenylacetic acid,dihydroxymandelic acid, etc. Salicylic acid is a preferred compound.

Suitable aliphatic and aromatic compounds which contain mono- andpolycarboxylic acid groups and one or more ether groups, amine groupsand/or thio groups typically contain from 2 to 20 carbon atoms,inclusive of the carbon atoms present in the carboxylic acid group(s).It is preferred that compounds containing mono- and polycarboxylic acidgroups contain from 2 to 20 carbon atoms and from 1 to 6 carboxylic acidgroups. Some examples of these compounds include mercaptoacetic acid,β-mercaptopropionic acid, thiosalicyclic acid, methoxyacetic acid,phenoxyacetic acid, 2-aminoacetic acid, 2-aminobenzoic acid,pyrrole-2-carboxylic acid, etc. Preferred compounds of this groupinclude methoxyacetic acid and thiosalicylic acid.

Carboxylic acids suitable for the present invention may be prepared byany of the known processes in the art. Examples of suitable processesare described in, for example, Kirk Othmer Encyclopedia of ChemicalTechnology, Fourth Edition, Vol. 5, pp. 168-178, and Vol, 11, pp.951-958. Formic acid, for example, may be prepared by the carbonylationof methanol using carbon monoxide.

In general, suitable aromatic amine group containing compounds of thepresent invention have molecular weights of less than about 500,preferably less than about 400, and more preferably less than 200.Suitable aromatic amine group containing compounds include, for example,those compounds wherein at least 1 amine group is, and preferably 1 to 3amine groups are, attached to an aromatic ring, and the aromatic ringmay be substituted or unsubstituted. Suitable substituents for thearomatic ring include, for example, alkyl groups having from 1 to 18carbon atoms which may be branched or linear such as, for example,methyl, ethyl, propyl, etc.; aromatic groups having from 6 to 13 carbonatoms such as, for example, phenyl, aminophenyl, and diaminophenyl; andarylalkyl groups having from 7 to 12 carbon atoms such as, for example,methylene(amino-phenyl), 2-(aminophenyl)butyl, etc. Suitablesubstituents for the aromatic ring also include hydroxyl groups.Amino-phenol is one example of a compound wherein the aromatic ring issubstituted with an hydroxyl group. Also, suitable as the aromatic aminegroup containing compound of the present invention are fused ringsystems containing from 10 to 20 carbon atoms. Diaminonaphthalene is oneexample of a suitable fused ring system for the present invention.

Examples of suitable aromatic amines for the present invention includecompounds such as aniline, diaminobenzene, triaminobenzene,tetraaminobenzene, tetraaminobiphenyl, methylene dianiline, crudetoluenediamine (i.e., a mixture of the various isomers), andortho-toluenediamine (i.e., an isomeric mixture of primarily 2,3-TDA and3,4-TDA in a weight ratio of about 60 to about 40). Ortho-toluenediamineand crude toluenediamine are preferred aromatic amines in the presentinvention.

The preparation of suitable amines for the present invention is wellknown to those skilled in the art. For instance, suitable amines can beprepared by dinitrating toluene with nitric acid in the presence ofsulfuric acid or other catalyst to yield isomers of dinitrotoluene,which are then reduced with hydrogen to yield crude toluenediamine.(See, for example, Kirk-Othmer Encyclopedia of Chemical Technology,Fourth Edition, "Amines by Reduction", Volume 2, pp. 483-501, and"Nitrobenzene and Nitrotoluenes", Volume 17, pp. 133-151.) Crude TDA isa mixture of the various isomers, i.e., 2,3-TDA, 2,4-TDA, 3,4-TDA,2,5-TDA, and 2,6-TDA.

In the process of the present invention, discoloration of aromaticamines is prevented or minimized by adding a small quantity of at leastone carboxylic acid containing from 1 to 20 carbon atoms to aromaticamines as soon as possible after the formation and subsequentpurification of these amines. The time after an amine is prepared andthe point in time at which the addition of a small quantity of acarboxylic acids is necessary to be effective in preventingdiscoloration of the amine ultimately depends on the stability of theparticular amine with respect to discoloration and how well it isprotected from contact with air.

Some relatively stable amines such as, for example, aniline, darkenslowly over time while other amines are relatively unstable and darkenimmediately upon exposure to air. Ortho-toluenediamine is one example ofa relatively unstable amine which darkens immediately when exposed toair. Accordingly, the point at which the stabilizing compound (i.e.,carboxylic acid) is added to the amine to prevent discoloration mayvary. It is, however, preferred that a small quantity of a carboxylicacid is added to the amine immediately following distillation. Thestabilizing compounds may be added at a later point, if the freshlyprepared amine is kept oxygen-free under an inert gas, such as, forexample, nitrogen or argon. Once the stabilizing compound(s) has beenadded to the aromatic amine compound, the resultant composition isrelatively stable in terms of color changes.

Typically, in a conventional process, when the nitrogen system fails ora leak occurs in the system protecting the amine group containingcompound from exposure to air, the amine group containing compoundbegins to darken. Ortho-toluenediamine and crude TDA, the preferredamine group containing compounds, start to darken immediately uponexposure to air. The presence of a stabilizing agent such as, forexample, formic acid, helps protect the color of the amine compounduntil the nitrogen can be restored.

It is, of course, possible to form polyether polyols wherein thepreviously described aromatic amines treated with a small quantity of atleast one carboxylic acid containing from 1 to 20 carbon atoms are theinitiators instead of conventional untreated aromatic amines. Apolyether polyol prepared from the color stable aromatic amine has alighter color than a polyether polyol prepared from an untreatedaromatic amine. Polyether polyols based on these treated aromatic amineinitiators in accordance with the present invention can be prepared byany of the known processes such as are described in, for example, U.S.Pat. Nos. 4,209,609 and 4,421,871, the disclosures of which are hereinincorporated by reference, and as described in British Patent 1,398,185.In general, the amine-initiated polyether polyols of the presentinvention are prepared by reacting an alkylene oxide with an aminehaving an amine functionality of at least 1, optionally in the presenceof an alkaline catalyst. Typically, up to 2 epoxide molecules can beadded to a primary amine group without the use of a catalyst. If,however, more than 2 epoxide groups per amine are desired, an alkalinecatalyst is generally used to promote the reaction.

The suitable amine initiators for preparing polyether polyols includethose previously described which have been treated with a carboxylicacid as described above. Some examples of alkylene oxides useful inproducing the polyether polyols of the present invention include:ethylene oxide, propylene oxide, butylene oxide, and mixtures of thesealkylene oxides. Combinations of ethylene oxide and propylene oxide areparticularly preferred. In principle, any alkaline material capable ofcatalyzing the epoxidation reaction of the present invention may beused. Specific alkaline catalysts which have been found to beparticularly suitable include, for example, potassium hydroxide andsodium hydroxide.

In general, the epoxidation reaction occurs by contacting the aminehaving an amine functionality of at least 1 with the alkylene oxide(s)at an elevated temperature in the range of from 90 to 180° C. undermoderately elevated pressure, optionally in the presence of the alkalinecatalyst. The amounts of amine and alkylene oxide which are used aregenerally 1 to 10 equivalents of alkylene oxide for each equivalent ofamine. The epoxidation product generally has an average hydroxyl value(determined by ASTM D-2849-69 hydroxyl number method C) of at least 28,preferably in the range of from about 250 to about 1200. The molecularweights of the polyether polyols of the present invention (numberaverage determined by end group analysis and nominal functionality ofthe polyol) preferably range from about 150 to about 1500, morepreferably from about 300 to about 1200, and most preferably from about400 to about 1000.

After the polyol has been prepared, the resultant reaction mixture whichcontains the alkaline catalyst in amounts of from about 0.1% to about1.0% as KOH is neutralized with an acid such as, for example, sulfuricacid, phosphoric acid, lactic acid or oxalic acid. Neutralization may beaccomplished by mixing the acid and reaction mixture at ambientconditions with stirring, then distilling to remove any excess water.The neutralized polyether polyol need not have a pH of exactly 7.0. Thereaction mixture may be maintained at a slight acidity or alkalinity,i.e., at a pH of from 5 to 11, preferably from 6 to 10. If the saltformed is soluble in the polyol, it may be left in. Otherwise, the saltcan be removed by, for example, filtration.

The neutralized polyether polyol reaction mixture of the presentinvention is clear, i.e., free from haze and may be used directly inprocesses for the production of polyurethane foams. Methods for theproduction of polyurethane foams by reacting these polyether polyolswith polyisocyanates via the polyisocyanate addition process are wellknown to those in the art.

The following examples further illustrate details for the preparationand use of the compositions and processes of this invention. Theinvention, which is set forth in the foregoing disclosure, is not to belimited either in spirit or scope by these examples. Those skilled inthe art will readily understand that known variations of the conditionsand processes of the following preparative procedures can be used toprepare these compositions. Unless otherwise noted, all temperatures aredegrees Celsius and all parts and percentages are parts by weight andpercentages by weight, respectively.

EXAMPLES

In the working examples of the present invention, the colors of treatedaromatic amine compounds were determined by a visual comparison with apink-red color scale. Reflectance values of this scale were determinedusing a Hunterlab Color Questll unit. In the untreated samples ofaromatic amine compounds, the color of the sample was too dark toaccurately measure reflectance values, so the color of these samples isreported as the Gardner color. The reflectance values are reported interms of L, a and b values for each sample.

Example 1

100 g. of freshly distilled ortho-toluenediamine (o-TDA) were placed ina bottle. To this, 0.6 g. of acetic acid was added, followed by mixingthoroughly. The sample was sealed, and placed in a 100° C. oven, alongwith a sealed sample of 100 g. of untreated, freshly distilledortho-toluenediamine (see Example 5 in Table 1). After 24 hours, theuntreated sample had a Gardner color >18, but the treated sample had acolor such that the reflectance values were L=49.31, a=46.90 andb=18.43. After 48 hours, the untreated sample of o-TDA was opaque black(i.e., the Gardner color was >18, whereas the sample treated with aceticacid still had a color such that the reflectance values were L=49.31,a=46.90 and b=18.43. After 1 week, the color of the o-TDA sample treatedwith acetic acid remained such that the reflectance values were L=49.31,a=46.90 and b=18.43.

Examples 2-4

These examples were performed using an essentially identical procedureas set forth under Example 1, with the exception of the particularstabilizing compound which was added to the freshly distilled o-TDA andthe amount of each stabilizing compound. Specific stabilizing compoundsand the relative quantity of each, as well as the result on thereflectance values of the color, or where appropiate, Gardner color,after storage in a 100° C. oven for 24 hours, 48 hours, and for 1 weekare shown.

                  TABLE 1                                                         ______________________________________                                        EFFECT OF TREATMENT OF O-TDA WITH ADDITIVES ON COLOR                                                Weight                                                    Example    Additive        (grams)   Reflectance Values                                                 .sup.(1)                                          ______________________________________                                        1      Acetic acid                                                                              0.6     L = 49.31; a = 46.90; b = 8.43                        2          Benzoic acid    1.2              L = 49.31; a = 46.90; b =                                 8.43                                                  3          Formic acid     0.5              L = 88.08; a = 4.26; b =                                  6.91                                                  4          Propionic acid  0.7              L = 49.31; a = 46.90; b =                                 8.43                                                  5          Untreated       --             >18 (opaque black).sup.(2)        ______________________________________                                         .sup.(1) represents Hunterlab Color QuestII reflectance values after          storage for 24 hours in a 100° C. oven. These reflectanoe values       were unchanged after storage in a 100° C. oven for 48 hours and        after 1 week.                                                                 .sup.(2) represents Gardner color after storage for 24 hours in a             100° C. oven.                                                     

Examples 6-7

100 g. of freshly distilled aniline were placed in a bottle. To this wasadded 0.5 g. of formic acid, followed by mixing thoroughly. The sample(Example 6) was sealed and placed in a 100° C. oven , along with asealed sample of 100 g. of untreated, freshly distilled aniline (Example7). After 7 days, the untreated sample had a Gardner color=16 (Example7), but the treated sample had a Gardner color=3.

Although the invention has been described in detail in the foregoing forthe purpose of illustration, it is to be understood that such detail issolely for that purpose and that variations can be made therein by thoseskilled in the art without departing from the spirit and scope of theinvention except as it may be limited by the claims.

What is claimed is:
 1. A process for stabilizing the color of anaromatic amine group containing compound, comprising:1) adding from0.001 to 10% by weight, based on 100% by weight of b), of a) at leastone organic compound containing at least one carboxylic acid group,wherein said organic compound containing from 1 to 20 carbon atoms, tob) an aromatic amine group containing compound.
 2. The process of claim1, wherein a) said organic compound containing at least one carboxylicacid group is an aliphatic compound having from 1 to 6 carboxylic acidgroups.
 3. The process of claim 2, wherein a) said organic compoundadditionally contains from 1 to 6 hydroxyl groups.
 4. The process ofclaim 1, wherein a) said organic compound containing at least onecarboxylic acid group is an aromatic compound containing from 7 to 20carbon atoms and having from 1 to 6 carboxylic acid groups.
 5. Theprocess of claim 4, wherein a) said organic compound additionallycontains from 1 to 5 hydroxyl groups.
 6. The process of claim 1, whereina) said organic compound containing at least one carboxylic acid groupis an aliphatic compound containing from 2 to 20 carbon atoms, havingfrom 1 to 6 carboxylic acid groups, and additionally containing one ormore ether groups, one or more amine groups and/or one or more thiogroups.
 7. The process of claim 1, wherein a) said organic compoundcontaining at least one carboxylic acid group is an aromatic compoundcontaining from 7 to 20 carbon atoms, having from 1 to 6 carboxylic acidgroups, and additionally containing one or more ether groups, one ormore amine groups and/or one or more thio groups.
 8. The process ofclaim 1, wherein a) said organic compound containing at least onecarboxylic acid group is an aromatic compound additionally containingone or more amine groups.
 9. A process for the production of a polyetherpolyol comprising alkoxylating an aromatic amine, wherein said aromaticamine is treated with from 0.001 to 5% by weight, based on 100% byweight of at least one organic compound containing at least onecarboxylic acid group, wherein said organic compound contains from 1 to20 carbon atoms.
 10. A stable aromatic amine composition comprising:a)from 0.001 to 10% by weight, based on 100% by weight of component b), ofan organic compound selected from the group consisting of acetic acid,formic acid, benzoic acid, propionic acid and mixtures thereof; and b)an aromatic amine group containing compound having a molecular weight ofless than about 500.